The Protected environment

Question 1

The Protected Environment

Answer 1

Protected cropping is the use of a structure to influence the environmental conditions so that negative aspects are reduced and positive factors enhanced.

Question 2

Sustainability and Environmental Impact of Protected Cropping

Answer 2

Protected cropping allows out-of-season production reducing the need for imported produce and associated transport effects and costs.
Manufacture of materials and structures to protect crops requires the use of much energy and often oil-based products e.g. plastics, glass, concrete, etc.
The environment created by structures is not necessarily attractive to wildlife.
The visual impact of protected cropping structures may not be positive.

Question 3

Different Structures

Answer 3

Structures used to protect plants usually consist of a framework supporting a transparent material or cladding. Such structures can be large enough to walk inside or they may protect an area maintained from outside the structure.

Examples include: Greenhouses, Polytunnels, Conservatories. Frames, Cloches (low polythene tunnels, units, individual e.g. bottles), Cupboard Frames

Question 4

Factors Affecting Plant Growth Changed by Protected Growing

Answer 4

The growth of plants under protection is affected by two main factors: the properties of the transparent material and the fact that the growing space is enclosed. They do this by influencing the following:

1) Light
2) Carbon Dioxide
3) Temperature
4) Air movement
5) Relative Humidity
6) Pests and Diseases

Question 5

Factors Affecting Plant Growth Changed by Protected Growing

1. Light

Answer 5

Structures reduce the amount of light reaching the plants inside with shading, reflection and the amount transmitted.
The ‘quality’ of the light is also altered – that is, the proportions of different wavelengths are changed.
These in turn have an influence on the rate of photosynthesis and certain morphological changes.
Sunlight entering a structure will also affect the temperature.

Question 6

Factors Affecting Plant Growth Changed by Protected Growing

2. Carbon Dioxide

Answer 6

The level of CO2 in a closed environment will often drop below that of the outside during the day. This will reduce the rate of photosynthesis.
Similarly, it can be affected by having a still layer of air outside the stomata, particularly in bright sunlight.
Carbon dioxide levels are affected, therefore, by air movement.

Question 7

Factors Affecting Plant Growth Changed by Protected Growing

3. Temp.

Answer 7

Temperature increases in protective structures due to the change in sunlight: from shorter to longer wavelengths once inside. These wavelengths cannot escape and this radiant heat raises the temperature compared to outside.
At colder times of the year, the temperature improvement has a considerable effect on plant growth.

Question 8

Factors Affecting Plant Growth Changed by Protected Growing

4. Air movement

Answer 8

With little air exchange with the outside, CO2 levels can become depleted, reducing the rate of photosynthesis. Humidity will increase and as a result cooling by transpiration is reduced and leaf temperatures can increase substantially.
Plants inside a structure are subject to less turbulent conditions than those outside and the temperature is able to rise.

Question 9

Factors Affecting Plant Growth Changed by Protected Growing

5. Relative Humidity

Answer 9

Humidity often increases in a closed structure. This reduces transpiration which itself reduces water stress. However, too little transpiration can mean there is no cooling effect in very hot conditions and the uptake of nutrients may also be affected.
High humidity may also increase the incidence of some fungal diseases.

Question 10

Factors Affecting Plant Growth Changed by Protected Growing

6. P&D

Answer 10

Certain conditions (warmth and humidity) can increase pests (reproduction rates of insects feeding on plants is increased with the increase in temperature) and diseases (fungal diseases spread faster) but the structure itself may exclude the arrival of spores or pests. For example, a closed structure can prevent access to flying insects.

Question 11

Structural and Cladding Materials

Greenhouses, Polytunnels, Frames and Cloches all have a framework upon which clear sheet material (cladding) is fixed or held

Answer 11

Steel - (used for some greenhouses, polytunnel hoops, the wire hoops of low, polythene cloches) Very strong, heavy / solid, long-lasting, little maintenance. Cold, bulky (= shade cast), expensive, may become rusty if galvanising deteriorates, heavy (problematic in construction or subsidence).

Aluminium - (greenhouses, frames) Light, quite cheap, no maintenance, long lasting. Can distort, not as strong, issues of sustainability.

Wood - (greenhouses, frames) Warm, aesthetically pleasing, renewable, potentially sustainable, easy to attach fixings. May require maintenance / can rot, bulky, expensive.

Plastic - (frames, ‘water-pipe’ hoops of cloches) Cheap, colourful(?), light, low maintenance. Prone to deterioration / short life, nasty, weak, can crack, oil-based product.

Question 12

Structural and Cladding Materials

Cladding is the transparent material used to influence the environment in protected environments

Answer 12

Glass - (greenhouses, frames, cloches) Easy to clean, good transparency, long-lasting, no discolouring, retains heat quite well. Breaks, heavy, requires strong structure, quite expensive.

Polyethylene Film / Polythene - (polytunnels, cloches) Cheap, flexible, quick to fit. Can deteriorate due to chemical sprays, can rip, short life span, may need skills to fit.

Polycarbonate - (greenhouses, frames, possibly cloches) Insulating (upto 45% cost reduction), rigid, safe, easy to cut, light, hail and vandal-proof, up to 20 yrs life. Quite expensive, can discolour, easy to scratch.

Acrylic - (greenhouses) Rigid, curved panels possible, light, safe. Discolours, easily scratched, expensive.

Question 13

Controlling protected environment - Light

Answer 13

Light transmission into a structure is affected by a number of factors.

1. The shape of the structure. Angled panes of glass or rounded structures allow more light to enter.
2. The site. Nearby structures must be at least 4 times their height distance away to minimise shading.
3. The orientation. An E-W orientation transmits more light in the winter: this is when light is possibly the factor limiting growth.
4. The cladding material and its condition. Glass and plastics have various light transmissions complicated by changes in opacity with time (including scratches) with plastics and the build-up of dirt and algal growth.

Given a particular shape and structure, how much light a plant receives can be manipulated in a number of ways.

Shading

This can be reduced by using a wider spacing of plants, particularly in the winter when light is at a premium.

Artificial shading can be used to reduce light, specifically, or as a side-effect of reducing the temperature. Often reduction is by 40-50%: cacti and succulents require little or no shading whilst ferns might need a 75% reduction.

• Washes: painted or sprayed on at the beginning of summer and cleaned off at the end. Inexpensive. Some types become more transparent when wet (i.e. lets in more light on cloudy/wet days. Messy.
• Blinds: provide adjustable shading, usually on the outside of a structure. Manual types need constant attention whilst automatic types are more convenient but expensive. Are often used to adjust daylength and so influence flowering e.g. Euphorbia pulcherrima (Poinsettia).
• Shading material: flexible mesh or woven materials. Usually fixed in place inside or out.

Lighting Equipment

Occasionally artificial light is the sole source for some plants e.g. specialist propagation units.

Usually, artificial light is supplementary: a top-up to winter or spring daylight either at either end of the day or during. Very useful with seedlings early in the year when many plants can be illuminated in a small area. Often used in conjunction with additional heating. Leads to a faster growth rate and better quality, sturdier plants.

The type of light has a bearing on which wavelengths are emitted and the quantity of each wavelength. Not all wavelengths are useful to plants. The most common bulbs in use are high-pressure sodium, fluorescent, compact fluorescent and LED. Different bulbs have different longevity, efficiency, output and cost.

Question 14

Controlling protected environment - Temp

Answer 14

Structures will, by themselves, raise the temperature inside by protection from wind chill, greenhouse effect, etc. This may be enough for some plants to maintain growth. Others will need to be frost free and some will be damaged even when the temperature is above freezing, like tomatoes, peppers, Saintpaulia, etc. In some cases, the temperature will get too high.

The temperature can be reduced using shading and ventilation.

Ventilation: the area covered by ventilators should be at least one sixth of the floor area. The principle behind ventilation is that warm, humid air is replaced by fresh air by:

• creating openings through which air can circulate. These should be staggered to ensure as much air circulation throughout the structure as possible. These could simply be lifting part of a structure as with cloches and frames, opening doors as in polytunnels or opening hinged vents and louvre ventilators in the walls or roofs of greenhouses. Relies on external air movement / wind or the ‘chimney effect’.
• using automated equipment to optimise the timing of ventilation. This includes automatic vent openers and extractor fans. The latter are usually set in the top of a greenhouse and a hinged louvre located at the bottom of the opposite wall to ensure maximum air movement.

The temperature can be raised or maintained using insulation or heating.

Insulation: usually used in conjunction with additional heating to reduce costs. The higher the temperature to be maintained, and the colder the region, the more cost-effective insulation is likely to be.

• double-glazing: very effective but expensive.
• plastic insulation: single sheets do not cut out much light but are not as effective as bubble plastic which consists of double or triple skins of transparent plastic with air cells in between.
• thermal screens: sheets of plastic or translucent material are drawn, like a curtain, across a structure to compartmentalise it or are drawn horizontally on wires across a greenhouse at eaves height in the evening. This reduces the volume requiring heating or insulating.

Heating: most protective structures are ‘cold’ i.e. unheated. However, in certain circumstances, some heating may be required, whether to raise the temperature to tropical conditions or just keep the space frost-free.

• in small structures, like cold frames, under soil heating cables can be used. These warm the whole structure but particularly the root zone so are useful for striking cuttings.
• Electric heaters: usually thermostatically controlled meaning heat is not wasted. Combined with fans these can also promote good air circulation and distribution of the warmth. Problems include installing an electricity supply, safety problems and the relatively low fuel efficiency of electricity.
• Gas heaters: from mains or bottled gas these have good fuel efficiency, can operate in isolation and may have a thermostat. However, bottled gas can run out and propane releases fumes and water vapour.
• Paraffin heaters: cheap to install, these heaters can work in the absence of mains connections. The lack of thermostats means they may be expensive to run. Also, water vapour and some plant-toxic fumes may be produced in combustion, fuel has to be transported and stored and maintenance is required (to check fuel levels and wick).
• Hot water pipes: old fashioned method involving a boiler and cast iron pipes. Modern versions.
• Hot beds: microbial activity in O.M. heats a heap and a frame set on top.

Question 15

Controlling protected environment - Humidity

Answer 15

The humidity – the amount of water vapour in the air – will affect the rate of transpiration. How plants react to different levels of humidity depends on the species. With some, a very high humidity will mean that low transpiration rates will not be present to cool the leaves and prevent damage from overheating. In other species, particularly tropical ones, a high humidity is essential to survive since they are not adapted to preventing the water loss that will occur in a dry atmosphere.

Warm air is capable of holding more moisture than cold air before it becomes saturated. Relative humidity describes the amount of water in the air as a % of the amount at saturation point for that temperature: the RH could be 50% at one temperature but there will be a lot more moisture in the atmosphere than an RH of 50% at a lower temperature. Most greenhouse plants benefit from an RH of between 75% and 40%. At levels above 80% Botrytis and Mildew can become a problem.

Humidity is reduced by ventilation.

It may be increased using various techniques: watering the floor and staging (‘damping down’) increases humidity.

Automatic spray systems can be used for plants that require very high and even humidity levels, also for cuttings.

Hand mist sprayers and water-filled trays will raise the humidity.

Question 16

Controlling the protected environment - Irrigation

Answer 16

By protecting plants with a structure, it gives the opportunity to control the water supply reaching plants. This brings its own problems, particularly with containers that can on the one hand need watering a number of times a day and on the other become waterlogged, particularly when temperatures are low and rates of photosynthesis are reduced.

Watering systems

Manual watering: watering cans, hoses.

Capillary systems: fine sand to a depth of 50mm with saturation at the base will keep pots moist that have been bedded into it.

Capillary matting ‘wicks’ the water from a reservoir. The compost in plastic pots will make good contact with this but clay pots may need a small piece of matting to act as a wick and connect the compost with the mat.

Overhead systems: overhead spraylines or sprinkler systems are used widely in large greenhouses and polytunnels. Rarely used in small structures.

Trickle irrigation: used for border crops in greenhouses and cloches etc. Water oozes out from along the length of a ‘seep’ hose or at specific points along it. There can be problems with little sideways movement in loose or sandy soils.

Drip irrigation: as with trickle irrigation, a pipe is fed from the mains or a reservoir. Narrow tubes branching off the pipe can be pegged down to deliver steady drips of water to just the base of plants. Often the nozzles on these tubes are adjustable.

Question 17

Controlling the protected environment - P & D

Answer 17

1) A protective structure by its nature is able to exclude some pests and diseases. Netting or mesh may be required to cover ventilation and / or doors should be kept closed.
2) Control ventilation to adjust humidity and reduce the incidence of fungal attacks.
3) Treated cladding materials can reduce certain wavelengths of light and prevent the spread of pests or the multiplication of diseases e.g. Sterilite polythene film.
4) Biological control is ideally suited to enclosed environments. Predators can be released in anticipation of a pest appearing, thriving in the warmer conditions and being unable to spread outside and be lost. Common controls in greenhouses and polytunnels include a mite Phytoseiulus persimilis for two-spotted spider mite, a parasitic wasp Encarsia formosa for whitefly and insect larvae and wasps for aphids.
5) Traps can be used but can be indiscriminate unless well positioned e.g. yellow sticky traps.
6) Chemical control is possible though most pesticides are harmful to biological controls, the exception is rapeseed oils against aphids and other small pests. Also chemicals can have a deleterious effect on polythene covers, shortening their life span.

Question 18

Containers Used in the Protected Environment

Answer 18

Sizes and Shapes

Standard – as deep as it is broad

Half Pots – ½ to 2/3 the depth of a standard pot (used for plants with small rootballs e.g. E/g Azaleas)

Pans – 1/3 the depth of a standard pot (used for seed sowing, alpines etc.)

Tubes, Long Toms – for deep rooted plants that would be restricted by a standard pot

Square / Round – round pots are traditional but square pots hold more compost for the same diameter and fit closer together, in that no gaps are left between. Round pots can actually take up less space: ‘pot thick’.

Colour - A range of colours can be found, though brown as an imitation of terracotta and black as an absorber of warmth are the 2 most common colours.

Material Plastic – light to handle (very important in certain places: shelving, balconies etc.). Inexpensive, Easy to clean, Durable – polypropylene alone may deteriorate in cold weather, impermeable so compost dries out more slowly. Oil-based product rarely made of recycled plastic. Clay - Heavy and stable so good for large, top heavy plants, Expensive but attractive. Difficult to clean, Breakable and often not frost resistant, Porous so plants are less likely to become waterlogged; may need more watering, Excellent for alpines because of extra drainage,

Other materials: Polystyrene – warm but bulky, also another oil-based product. Peat pots – whole pot can be planted out; unsustainable product. Paper – can be home made, recycling paper; not so easy to fill. Glazed pots – often clay, making them less porous and more colourful. Improvised – any container that can hold compost and provide drainage can be considered e.g. old tins, boots, etc. Wooden – excellent for large plants e.g. barrels; rot and woodlice can be problems.

Question 19

Cell & Seed tray

Answer 19

Seed tray

Advatnage, Quick to sow, uses less compost, uses less space.

Disadvantage, Longer to plant up, roots disturbed, damping off more likely, easy to overcrowd.

Cell or module tray

Advantage, no root disturbance, more compost per plant, doesn’t waste expensive seed, saves compost when few seeds sown.

Disadvantage, Equip. can be more expensive, compost is wasted if cell has no show, takes up more space, slower to sow into.

Question 20

Containers for display

Answer 20

Management Considerations

Size: the volume will affect the amount of watering and feeding required.

Colour: black absorbs heat.

Drainage: adequate holes? Sleeves.

Material: terracotta leads to drier compost (e.g. cacti), plastic gives a damper compost (e.g. ferns).

Space: available room.

Reservoir: ‘self-watering’ pots.

Portability: size, weight, material.

Durability

Visual Appeal

Colour: matching, blending, cohesive, identical?

Style

Shape

Patterns

Weathering

Ease of cleaning

Question 21

Care of pots

Answer 21

Feeding

In established pot plants, feeding is almost exclusively as a liquid fertilizer. This combined with the nutrients released from fresh compost used as a top dressing or with which to pot on will normally be the only source of nutrients. Occasionally, slow or controlled release pellets can be inserted. The formulation of a feed should reflect the requirements of the plant. For example, a flowering plant could be fed with a high potassium feed like comfrey liquid whilst a foliage plant would be better with a more balanced fertilizer or one containing a good percentage of nitrogen like wormery liquid.

Irrigation

Watering requirements will vary throughout the year and will depend on the plant species. In the winter, with lower temperatures and light levels, less will be required.

Knowledge of the compost will help since different types have different properties. Coir based composts can appear dry on the surface whilst underneath there is sufficient moisture. Peat based composts are hard to re-wet once dry, so they need constant checking.

Watering should be thorough, possibly, in the case of some rot-sensitive plants like cyclamen, from below: water should be added to the saucer and any still left after half an hour should be tipped away.

Rainwater or distilled water is preferable for many pot plants, and for acid-loving plants it is essential.

Mulching

This is often not possible without first removing some compost or if the level has dropped. With pots this is known as top dressing and is often used on large pots where re-potting is difficult or with plants that react badly to root disturbance and / or prefer confined roots

Question 22

Growing medium for pots

Answer 22

Choice of Growing Medium

These can be divided into those containing a mineral fraction (loam-based composts) and those not (loam-less potting composts).

Loam-Based Compost:

Provides the best conditions for long term growth. It contains a steady supply of nutrients and has a good structure: free-draining and aeration. They are less prone to drying out and water logging. Plants apparently adapt better to being planted out into garden soil if first raised in loam-based compost.

Loamless Compost:

Lightweight and clean. Depending on the source of the organic base e.g. peat, moisture retention and aeration are usually good. However, the nutrient status is low. Some types are prone to breaking down rapidly so that the volume of compost shrinks and the remaining material loses much of its structure. Therefore, for long term composts, a more fibrous base is desirable. If overwatered, loam-less compost tends to become waterlogged.

Specialist composts: loam-based with added grit and low nutrient status for alpines and cacti. Bark particles for free-drainage and low nutrients (often plus charcoal) for orchids. Ericaceous composts are used for acid-loving / lime-hating plants e.g. Azaleas. Bulb fibre is un-decomposed sphagnum moss to provide an open structure for growing in containers without drainage holes – feel free to ask why this is necessary. Nutrients are not supplied since bulbs have their own food source.

Question 23

The Protected environment

Pot Cyclamen persicum

Answer 23

Propagation = Seed / divide. Soak & sow seed late summer 21^o

Potting = loam based compost + grit

Feeding = once every 2 weeks with general house fertiliser

Watering = keep moist, water from bottom of plant and mist, reduce after flowering.

Thin/Tying /Staking = n/a

Harvest = seed collection late summer

Pruning = Dead head flowers & old foliage by twist and pulling

P&D Ident & Control = Grey mould on leaf and crown from humidity and over watering. Cylcamen mite - destroy leaf.

Question 24

The Protected environment

Salad Solanum lycopersicum
in greenhouse

Answer 24

Propagation = from seed in Feb-Mar 20^o

Potting = 9cm pot +1 month plant out +1 month

Feeding = from first flower every 2 weeks high potassium feed

Watering = Lots of water, regular and steady

Thin/Tying /Staking = Wind around support string or tie to cane

Harvest = As required for use when fruit has some ‘give’

Pruning = Junction between leaf and stem. Pinch and break off.

P&D Ident & Control = Blight, white fly and greenfly. Blight resistant variety ‘Crimson crush’

Question 25

The Protected environment

Bedding Impatiens walleriana

Answer 25

Propagation = hard from seed. Sow in march 21^o

Potting = pot on in April, and transplant in late may.

Feeding = Peat free compost. From mid summer liquid feed high in potash every 2 weeks.

Watering = moist well drained

Thin/Tying /Staking = n/a

Harvest = n/a

Pruning = trim straggly shoots and dead head.

P&D Ident & Control - impatiens mildew, don’t get water on foliage. Leaf turn yellow and drop. Plant resistant cultivar.

Question 26

The Protected environment

Cut Chrysanthemum x moriifolium

Answer 26

Propagation = basal softwood cutting with root in spring

Potting = 30cm diameter pot, John Innes 2

Feeding = general feed, from end of april. Weekly high in potassium when in flower

Watering = regularly

Thin/Tying /Staking = tie to cane at 20cm

Harvest = cut formed bud 23/30cm

Pruning = remove lateral buds and shoots

P&D Ident & Control = slug, snails, eel worms, capsid bug.
White rust, grey mould ear wig.

Question 27

The Protected environment

Bulb for forcing Narcissus ‘Tete a tete’

Answer 27

Propagation = Collect offsets pull apart. In pots in cold and dark, 1 month until flower.

Potting = potting medium then lay bulbs, and top up with compost, tips just showing and same as top of pot

Feeding = n/a

Watering = very little watering required

Thin/Tying /Staking = n/a

Harvest = n/a

Pruning = Dead head flowers to produce more offsets, remove leaf when fallen.

P&D Ident & Control = narcissus fly. Root rot/basal rot caused by over watering fungus. Nematodes, eel worm.

Question 28

Horticultural Uses of the Protected Environment

Answer 28

Protected environments like greenhouses, polytunnels, conservatories and cold frames can be used in a number of ways such as over-wintering: even if there is no heating in the structure, protection from wind and excesses of frost will be useful for a range of plants e.g. Citrus sp., Fuchsia sp., Pelargonium sp.

They are also very useful in the production of plants: the elevated temperatures will particularly give a more even germination. This can include vegetables, bedding plants, etc. and is often in containers. However, seeds are frequently sown in the soil of cold frames to raise plants for planting out.

Greenhouses and especially conservatories are used to display plants – often these are flowering, tender plants.

Question 29

The Protected environment

Adiantum raddianum - maidenhair fern

Answer 29

Adiantum raddianum - maidenhair fern

Propagation - Division with knife. Rhizome

Light - Good, indirect, N. windowsill.

Humidity - High

Feeding - Half dose, fortnightly.

Watering - Always keep moist.

Re-potting - Keep slightly under potted. Young vigorous plant annually.

Deadheading etc - N/A

Question 30

The Protected environment

Ficus benjamina - Weeping fig

Answer 30

Ficus benjamina - Weeping fig

Propagation - Softwood stem cuttings

Light - Bright E or W in summer, S in winter.

Humidity - Mist occasionally.

Feeding - Fortnightly.

Watering - Allow some drying between.

Re-potting - Every 2 years until large

Deadheading etc - N/A

Question 31

The Protected environment

Euphorbia pulcherrima - Poinsettia

Answer 31

Euphorbia pulcherrima - Poinsettia

Propagation - Stem cuttings

Light - Indirect in summer, max in winter.

Humidity - Frequent misting in flower.

Feeding - Fortnightly.

Watering - Thorough watering, then moderately dry, more in summer.

Re-potting - Annual in May.

Deadheading etc - After leaf fall, cut to 10cm, keep dry, shady and mild until May. End of Sept. give 14hrs dark per day for 8 weeks.

Question 32

The Protected environment

Kalanchoe blossfeldiana - Flaming katy

Answer 32

Kalanchoe blossfeldiana - Flaming katy

Propagation - Stem cuttings.

Light - Bright E or W in summer, S in winter.

Humidity - N/A

Feeding - Monthly

Watering - Thorough watering, then moderately dry, more in summer.

Re-potting - Annual after rest period.

Deadheading etc - After flowering cut back tops and leave un-watered for a month.

Question 33

The Protected environment

Saintpaulia ionantha - African Violet.

Answer 33

Saintpaulia ionantha - African Violet.

Propergation - Leaf petiole cuttings.

Light - Bright E or W in summer, S in winter.

Humidity - High, using a pebble tray.

Feeding - Monthly.

Watering - Keep moist, not on leaf, occasionally by immersion.

Re-potting - Moderately pot bound, spring when necessary.

Deadheading etc - Remove dead flowers complete with stalk.